Speaker grill

ABSTRACT

A speaker grille disposed in front of a speaker having a diaphragm and reproducing the sounds of 1 kHz and higher. The speaker grille is provided with a sound opening which includes a line that opposes to a region extending from the edge portion of a diaphragm to the fixing portion on the outer circumference of the diaphragm of speaker. The speaker grille offers superior sound characteristics, at the same time a sufficient mechanical strength either.

TECHNICAL FIELD

The present invention relates to a speaker grille attached to a cabinet,etc. for combination with a speaker.

BACKGROUND ART

A speaker grille is designed so that it has a sufficient mechanicalstrength needed for protecting a speaker from damage, at the same timeit has to provide a speaker with an opening that is large enough not toill-affect the quality of reproduced sounds. For those speakers whosediaphragm areas are small, among other speaker types, new structureshave been proposed for their speaker grilles in order to reduce an areawhich blocks diaphragm region to a minimum, while securing a sufficientmechanical strength. Japanese Patent Unexamined Publication No.2003-37883 discloses a conventional speaker grille 91 as shown in FIG.27; which speaker grille is disposed in front of speaker 92, andprovided with sound openings 93 whose open rates are uneven.

Speaker grilles require quite a high open rate for not retarding soundvibration of speakers. The main sound openings are disposed in an areacorresponding to the central region of a diaphragm, where the soundpressure level is high. Describing more practically, the sum area ofsound openings has to be at least 60%, if the characteristics have to bekept within approximately −6 dB for the sounds of 5 kHz and higher. Thesmaller the speaker size is, the higher the open rate is required forthe speaker grille.

FIG. 28 is a sound characteristics chart of a speaker combined with aspeaker grille whose open rate is as low as 28%. In the chart, the solidline represents sound characteristics 95 with no speaker grilleattached, while the dotted line represents sound characteristics 96 withthe speaker grille attached. The sound pressure level is lower in thevicinity of 5 kHz and of 10 kHz with sound characteristics 96 shown indotted line, as compared with characteristics 95. On the other hand,sound characteristics 96 exhibit higher sound pressure level in thevicinity of 3 kHz; which is due to resonance. Thus, design in the soundopenings of a speaker grille gives significant influence to thecharacteristics of sounds of a speaker combined with the speaker grille.

The intrinsic task of a speaker grille is to protect a speaker fromdamage, so it has to have a certain mechanical strength. Therefore,there is a limitation to making the size of sound opening larger. Thespeaker grille as shown in FIG. 27 secures a certain open rate byproviding rectangular sound openings in the area opposing to diaphragmedge, in addition to the area opposing to the central part of diaphragm.This configuration, however, requires a certain thickness for ensuring arequired mechanical strength. This means that it is not suitable for usewith the small-size speakers, among other types of speakers.

DISCLOSURE OF INVENTION

A speaker grille in the present invention is disposed in front of adiaphragm speaker which reproduces the sounds of 1 kHz and higher. Thespeaker grille includes a line which opposes to a region from the edgeportion of a speaker diaphragm to the fixing portion on the outercircumference of the diaphragm. The speaker grille provides superiorsound characteristics, at the same time a sufficient mechanical strengtheither.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view showing a speaker grille in accordancewith a first exemplary embodiment of the present invention, and aspeaker connected with the speaker grille.

FIG. 1B is a cross sectional view showing a key part of the speakershown in FIG. 1A.

FIG. 1C is a cross sectional view showing a key part of another speakercoupled with the speaker grille of FIG. 1A.

FIG. 2 shows sound characteristics exhibited by a combination of thespeaker grille and the speaker of FIG. 1A.

FIG. 3 shows sound characteristics exhibited by a combination of aspeaker grille having a sound opening at the center and the speaker ofFIG. 1A.

FIG. 4 shows sound characteristics exhibited by the speaker of FIG. 1Awhich is blocked to be half in the direction of the major axis.

FIG. 5 shows sound characteristics exhibited by the speaker of FIG. 1Awhich is blocked to be half in the direction of the minor axis.

FIG. 6 shows sound characteristics exhibited by a combination of thespeaker grille and the speaker of FIG. 1A.

FIGS. 7 through 9 show sound characteristics exhibited by the speakergrille of FIG. 1A, with different open rates.

FIG. 10 is a perspective view showing a speaker grille in accordancewith a second exemplary embodiment of the present invention and aspeaker connected with the speaker grille.

FIG. 11 shows sound characteristics exhibited by a combination of thespeaker grille and the speaker of FIG. 10.

FIG. 12 shows sound characteristics exhibited by a combination of aspeaker grille having a sound opening at the center and the speaker ofFIG. 10.

FIG. 13 is a perspective view showing a speaker grille in accordancewith a third exemplary embodiment of the present-invention and a speakerconnected with the speaker grille.

FIG. 14 shows sound characteristics of the speaker of FIG. 13 which isblocked to be half in the direction of major axis.

FIG. 15 shows sound characteristics of the speaker of FIG. 13 which isblocked to be half in the direction of minor axis.

FIG 16. shows sound characteristics exhibited by a combination of thespeaker grille and the speaker of FIG. 13.

FIGS. 17 through 19 show sound characteristics exhibited by the speakergrille of FIG. 13 with different open rates.

FIGS. 20 through 22 show the structures of other speaker grilles in thethird embodiment of the present invention.

FIG. 23 shows sound characteristics exhibited by a combination of thespeaker grille in FIG. 20 and the speaker in FIG. 13.

FIG. 24 shows sound characteristics exhibited by a combination of thespeaker grille in FIG. 21 and the speaker in FIG. 13.

FIG. 25 shows sound characteristics exhibited by a combination of thespeaker grille in FIG. 22 and the speaker in FIG. 13.

FIG. 26 is a cross sectional view showing a state of an exemplarycombination where the speaker in FIG. 13 is connected with either one ofthe speaker grilles in FIGS. 20 through 22.

FIG. 27 shows a structure of a conventional speaker grille.

FIG. 28 shows sound characteristics exhibited by a conventionalconfiguration in which the open area is reduced.

DETAILED DESCRIPTION OF PREFERRED EMBODIEMNTS

Exemplary embodiments of the present invention are described in thefollowing with reference to the drawings. In each of the followingembodiments, those portions having the identical structures as those ofpreceding embodiments are represented by using the identical symbols,and detailed description on such portion is sometimes eliminated. It isto be noted that the descriptions of embodiments are just exemplary;they should not be interpreted to limit scope of the invention.

First Exemplary Embodiment

FIG. 1A is a perspective view showing a speaker grille in accordancewith a first exemplary embodiment of the present invention and a speakerconnected with the speaker grille. FIG. 1B is a cross sectional view ofthe speaker shown in FIG. 1A. Speaker 1 is provided with diaphragm 6which forms an oval vibration plane with the major axis of 12 cm and theminor axis of 8 cm. Diaphragm 6 is fixed at the outer circumference toframe 7 and gasket 100. Speaker grille 3 is disposed in front of speaker1, and fixed to frame 7 which covers diaphragm 6. Speaker grille 3 maybe made of an acrylic resin or the like resin, aluminum or other metalmaterial, using a cutting process or a die-molding process. Speakergrille 3 has a thickness of about 0.1-10 mm. Speaker grille 3 may beformed as an integral part of a cabinet for television receiver, radioreceiver or the like audio apparatus; there is no specific limitation tothe material used, it may be provided by cutting a wooden material, forexample.

Speaker grille 3 is provided with sound openings 2, which is divided byreinforcement rib 5 disposed for ensuring a certain mechanical strengthover the entire speaker grille 3. Each of sound openings 2 includes line8 that is opposing to a region from edge portion 4A of diaphragm 6 tofixing portion 4 on the outer circumference of diaphragm 6. Each soundopening 2 has arc-curved portion 9 that is in parallel with fixingportion 4 on the outer circumference of diaphragm 6. By forming soundopenings 2 in the above-described manner so that they include arc-curvedportions 9 proceeding along fixing portion 4 on the outer circumference,sound openings 2 are provided so that it contains, to the maximumextent, the area opposing to edge portion 4A. In the example shown inFIG. 1A, curved portion 8 is shown in coincidence with fixing portion 4;so, the line opposing to a region from edge portion 4A to fixing portion4 on the outer circumference of diaphragm 6 can be explicitly recognizedas line 8. However, the perforated area of sound opening 2 may includesuch line which we sometimes fail to explicitly recognize.

Here, the terminology “fixing portion 4 on the outer circumference ofdiaphragm 6” signifies the inner circumference line of gasket 100, thegasket being provided at the outer circumference of edge portion 4A. Ina case where the speaker is not provided with a gasket as shown in FIG.1C, the terminology indicates the inner circumferential line of frame 7locating at the outside of edge portion 4A. In any case, fixing portion4 signifies the outermost circumference of a vibration plane whichvibrates when speaker 1 generates sounds. However, since the mainvibration part is at a place inner than the outer circumference of edgeportion 4A, it is preferred that sound opening 2 include a line thatopposes to outer circumference 4B of edge portion 4A.

Sound characteristics exhibited by a combination of the above-configuredspeaker grille 3 and speaker 1 are shown in FIG. 2. Meanwhile, soundcharacteristics exhibited by a combination of a speaker grille having around opening of the same square measure as that of sum of soundopenings 2 at the center to be concentric with diaphragm 6 and speaker 1are shown in FIG. 3. In either of the above combinations, there is noserious difference between characteristics curve 11 representing thesounds without a speaker grille and characteristics curves 12, 13representing the sounds with the speaker grilles attached, in so far asthe sound region lower than 1 kHz is concerned. Characteristics curve13, however, shows resonance in the vicinity of 1-2 kHz and in thevicinity of 4 kHz, and, as a reaction to it, the harmoniccharacteristics deteriorate. On the other hand, characteristics curve 12indicates a significant improvement with respect to the characteristicsdeterioration. These teach us that even if sum of the square measure ofthe sound openings is equal, the speaker grille generates resonance whenthe area opposing to edge portion 4A is blocked; furthermore, thecharacteristics deteriorate in the high sound region of 9 kHz or higher.Therefore, it is preferred that a speaker grille be designed into such astructure as shown in FIG. 1A. Thus, speaker grille 3 brings about anadvantage for those speakers which reproduce the sounds of 1 kHz andhigher.

Next, the sound characteristics are compared using speaker grilles eachhaving a 50% open rate; between a combination with speaker 1 blocked tobe half in the direction of the major axis and speaker 1 blocked to behalf in the direction of the minor axis. The respective soundcharacteristics are shown with characteristics curve 14 in FIG. 4 andcharacteristics curve 15 in FIG. 5. Here, the terminology “open rate”stands for a proportion of effective open area provided by soundopenings 2 against a projected area of diaphragm 6. In a case where partof sound openings 2 coincide with fixing portion 4, as shown in FIG. 1A,or a case where sound openings 2 are disposed to be inner than fixingportion 4, the effective open area is sum of the square measure of soundopenings 2 itself. On the other hand, in a case where any of soundopenings 2 include the portion that is opposing to fixing portion 4, theeffective open area is sum of the area of sound openings 2 minus asquare measure blocked by gasket 100 or frame 7.

The sound characteristics exhibited by a combination of speaker grille 3having the same open rate as described above in the same pattern asshown in FIG. 1A and speaker 1 are shown with characteristics curve 16in FIG. 6. Both FIG. 4 and FIG. 5 exhibit resonance; this is because, asalready described earlier, a substantial part of an area opposing toedge portion 4A is blocked. On the other hand, characteristics curve 16exhibits superior characteristics with the resonance suppressed, ascompared with characteristics curves 14 and 15.

Now in the following, description is made on the change of soundcharacteristics caused as the result of varied open rate, whichvariation in the open rate is devised by changing width 2A of soundopenings 2. Characteristics curve 17 in FIG. 7 represents the soundcharacteristics when width 2A is 5 mm, whereas characteristics curve 18in FIG. 8 represents those when width 2A is 10 mm. The greater the width2A is, the better the sound characteristics are. Characteristics curve19 in FIG. 9 which represents an example where width 2A is 15 mm issubstantially identical to curve 16 in FIG. 6; deterioration in thecharacteristics is suppressed to be approximately −3 dB in the soundregion of 1 kHz or higher. The open rate of the example is 31%. Namely,the open rate should preferably be at least 31%. From the view point ofmechanical strength of speaker grille 3, the open rate should preferablybe lower than 60%.

Second Exemplary Embodiment

FIG. 10 is a perspective view showing a speaker grille in accordancewith a second exemplary embodiment of the present invention and aspeaker connected with the speaker grille. Speaker 1 is provided withdiaphragm 6 which forms a round vibration plane of 8 cm diameter. Therest parts of the structure remains the same as those in the firstembodiment.

Sound characteristics exhibited by a combination of the above-configuredspeaker grille 3 and speaker 1 are shown in FIG. 11. Meanwhile, FIG. 12shows sound characteristics exhibited by a combination of a speakergrille which is provided with, instead of sound openings 2, a roundopening of the same square measure as sum of sound openings 2 disposedto be concentric with the center of diaphragm 6, and speaker 1. Ineither of the above combinations, there is no serious difference betweencharacteristics curve 20 representing the sounds without a speakergrille and characteristics curves 21, 22 representing the sounds withthe speaker grilles attached, in so far as the sound region lower than 1kHz is concerned. Characteristics curve 22, however, shows resonance inthe vicinity of 1-2 kHz and in the vicinity of 5 kHz; and, as a reactionto it, the harmonic characteristics deteriorate. On the other hand,characteristics curve 21 indicates a significant improvement withrespect to the characteristics deterioration. Thus, even if sum of thesquare measure of the sound openings is equal, the speaker grillegenerates resonance and results in a substantial deviation from aspeaker's own sound characteristics when the area opposing to edgeportion 4A is blocked. Therefore, it is preferred that speaker grille bedesigned into such a structure as shown in FIG. 10. Preferred open ratein the present embodiment is at least 31% and lower than 60%, whichbeing the same as that described in the first embodiment. Detaileddescription on which is eliminated here.

Third Exemplary Embodiment

FIG. 13 is a perspective view showing a speaker grille in accordancewith a third exemplary embodiment of the present invention and a speakerconnected with the speaker grille. Speaker 1 measures 73 mm in thelonger side and 17 mm in the shorter side, which is provided withdiaphragm 6 of oblong vibration plane. Diaphragm 6, made of a polyimideor the like resin film, is fixed at the circumference with frame 7.Speaker grille 3 is disposed in front of speaker 1, and fixed to frame 7covering diaphragm 6.

Speaker grille 3 is provided with sound openings 2, which are divided byreinforcement ribs 5 and block portion 5A; reinforcement ribs 5 aredisposed for ensuring a certain mechanical strength over the wholespeaker grille 3, and block portion 5A blocks the central region ofvibration plane. Block portion 5A protects the central area of diaphragm6. Each of sound openings 2 includes line 8 that is opposing to a regionfrom edge portion 4A of diaphragm 6 to fixing portion 4 on the outercircumference of diaphragm 6. Sound openings 2 at both ends havearc-curved portion 9 which are in parallel with fixing portion 4 on theouter circumference of diaphragm 6. By forming sound openings 2 in theabove layout where it includes curved portion 9 along fixing portion 4at the outer circumference, sound openings 2 can be provided to contain,to the maximum extent, the area opposing to edge portion 4A.

Sound characteristics exhibited by a combination of the above-configuredspeaker grille 3 and speaker 1 are shown with characteristics curve 26in FIG. 16. The open rate against the cross sectional area of vibrationplane is 47%, in the present case. Meanwhile, sound characteristicsexhibited by a combination with a speaker grille of the same open rateblocking half of speaker 1 in the direction of the longer side are shownwith characteristics curve 24 in FIG. 14, and those with a speakergrille blocking half of speaker 1 in the direction of the shorter sideare shown with characteristics curve 25 in FIG. 15. In either of theabove charts, characteristics curve 23 represents those without speakergrille 3.

Characteristics curve 24 shows resonance. This is due to the largeblocking area opposing edge portion 4A. On the other hand, the resonanceis suppressed in characteristics curves 25 and 26. The reason why theresonance is suppressed in curve 25 seems to be in the fact that thesize of speaker 1 in the present embodiment is smaller than thecounterparts in the first and the second embodiments. In the soundregion of 5 kHz-10 kHz, however, curve 26 exhibits a profile which iscloser to curve 23 than that of curve 25; which means curve 26 is morefavorable.

Next, change in the sound characteristics caused by varied open rate,devised by changing widths 2A, is described. Characteristics curve 27 inFIG. 17 exhibits the sound characteristics when width 2A is 2 mm,whereas characteristics curve 28 in FIG. 18 exhibits those when width 2Ais 3 mm. As can be understood from the charts, the sound characteristicsimprove along with the increasing width 2A. Characteristics curve 26 inFIG. 16 represents the result where width 2A is 4 mm; the curve issubstantially identical to curve 29 in FIG. 19, which represents theresult where width 2A is 5 mm. In the above two curves, deterioration ofthe characteristics is suppressed to be approximately −3 dB in the soundregion of 1 kHz or higher. The open rate in this case is 47%, as alreadydescribed earlier. Namely, the open rate is preferably at least 47%.Whereas from the view point of ensuring a certain mechanical strengthwith speaker grille 3, the open rate is preferably lower than 60%.

Now in the following, description is made on variations in the shape ofspeaker grille 3 connected to the so-called slim-type speaker 1 of FIG.13. FIG. 20 shows a variation of speaker grille 3; sound openings 2 areprovided only in the area corresponding to edge portion 4A,reinforcement rib 5B is provided in parallel with the longer sides ofvibration plane and is located at the center in the direction of theshorter sides of vibration plane, so that it separates two soundopenings 2 in the direction of the shorter sides of vibration plane.Namely, one reinforcement rib 5B is formed laterally with an approximatewidth of 6 mm expanding equally from the central line towards up anddown.

FIG. 21 and FIG. 22, respectively, show other exemplary variations ofspeaker grille 3; they are provided with a plurality of reinforcementribs 5 disposed in parallel with the shorter sides of vibration planefor further splitting the two sound openings, further to theconfiguration shown in FIG. 20. Namely, rib 5B is formed laterally withan approximate width of 6 mm expanding equally from the central linetowards up and down. In addition, sound openings 2 having an approximatewidth of 14 mm and ribs 5 having an approximate width of 2 mm arealternately disposed in the right-left direction with equal orientationfrom the central line for as long as approximately 50 mm in the laterallength and the sets of the openings and ribs are disposed in alongitudinal direction, in FIG. 21. In FIG. 22, with equal orientationfrom the central line in the lateral direction, sound openings 2 havingan approximate width of 4 mm and ribs 5 having an approximate width of 4mm are disposed alternately with equal orientation from the central linein the lateral direction. The open rate in FIG. 20, FIG. 21 and FIG. 22are 48%, 28% and 22%, respectively. Sound characteristics of thesespeaker grilles 3 connected with speaker 1 of FIG. 13 are shown in therespective charts shown in FIG. 23, FIG. 24 and FIG. 25. In each of thecharts, solid line curve 31 represents the characteristics without aspeaker net, while dotted line curves 33, 34 and 35 exhibit those with aspeaker net.

In the combination corresponding to FIG. 23, open rate of 48% is securedagainst the aperture area of the speaker. Therefore, the characteristicscurve 33 shows hardly any deviation from the original characteristicscurve 31. In the combination corresponding to FIG. 24, the open rate is28% against the aperture area of the speaker; therefore, thecharacteristics are inferior as compared to characteristics curve 33,but the characteristics deterioration is suppressed to be approximately−3 dB in the sound region of 8 kHz or higher. In the combinationcorresponding to FIG. 25, the open rate is 22% against the aperture areaof the speaker; therefore, the characteristics are inferior compared tocharacteristics curve 33, but the characteristics deterioration issuppressed to be approximately −6 dB in the sound region 5 kHz orhigher.

Furthermore, it is preferred to provide magnet 43 on speaker grille 3 atthe surface facing to diaphragm 6, as illustrated in FIG. 26, a crosssectional view. Speaker 1 has flat voice coil 42 disposed on diaphragm 6at the location opposing to magnet 41. Magnet 43 can be attached toblock portion 5A or rib 5B. Further, yoke 44 may be provided in order tohave magnetic flux of magnet 43 more concentrated.

Magnet 43 is disposed to oppose magnet 41 in a repulsive polarityarrangement. With such a configuration, direction of generated magneticflux is orientated to be horizontal and the electric current travelingin coil 42 makes a perpendicular crossing with the magnetic flux. Thisenhances the magnetism efficiency.

Although sound openings 2 in each of the above embodiments are describedin a shape that it is surrounded with an arc curve or a straight line,it is not the intension of the present invention to limit the shape ofsound opening 2 as such. Sound openings 2 may be provided in whatevermanner so far as they are formed in an area within the inside of line 8and they include line 8; the line is facing the region extending fromedge portion 4A of speaker 1 to fixing portion 4 on the outercircumference of diaphragm 6.

Although sound openings 2 in each of the above embodiments are describedthat they include a line opposing to fixing portion 4 on the outercircumference, it is not the intension of the present invention to limitit as such. For example, sound openings 2 may be provided in such amanner where they include a line which is opposing to the innercircumference of edge portion 4A and are formed to be inner than theline. With this configuration, the advantage of the present inventioncan be implemented to some extent. Especially with those speakers oflarge aperture diameter, even a sound opening provided in an area innerthan the inner circumference of edge portion 4A can ensure satisfactorysound characteristics. With the speakers of small aperture diameter,however, deterioration in the sound characteristics is significant ifthere is no sound opening 2 in front of edge portion 4A. So, it ispreferred to provide sound opening 2 in a manner that it includes a linewhich is facing a virtual line locating at least 3 mm inner from theouter circumference of edge portion 4A. The approximate distance of 3 mmcan offer an advantage that is identical to that described in theembodiments of the present invention.

INDUSTRIAL APPLICABILITY

A speaker grille of the present invention is disposed in front of aspeaker having a diaphragm and reproducing the sounds of 1 kHz orhigher. The speaker grille is provided with a sound opening whichincludes a line opposing to a region extending from the edge portion ofthe diaphragm to the fixing portion on the outer circumference of thediaphragm. The sound opening is provided only in an area inner than theline. The above-configured speaker grilles offer practical advantageswhen used as the sound aperture for acoustic apparatus which includes aspeaker.

1. A speaker grille provided with a sound opening, the speaker grillebeing fixed at a fixing portion on the outer circumference and disposedin front of a speaker comprising a diaphragm including an edge portion,the speaker reproducing sounds of 1 kHz and higher; wherein the speakergrille is provided with a reinforcement rib opposing to a central partof the speaker, and the sound opening includes a line opposing to aregion extending from the edge portion of the diaphragm to the fixingportion on the outer circumference.
 2. The speaker grille of claim 1,wherein the sound opening includes a line opposing to the outercircumference of the edge portion of the diaphragm.
 3. The speakergrille of claim 1, wherein the speaker is provided with one of a roundvibration plane and an oval vibration plane, the sound opening includesan arc-shape curve in parallel with the fixing portion on the outercircumference.
 4. The speaker grille of claim 1, wherein the soundopening is one of a plurality of sound openings, the reinforcement ribhas a portion for separating the sound openings.
 5. The speaker grilleof claim 1, wherein the speaker is provided with one of a roundvibration plane and an oval vibration plane, an effective open area ofthe sound opening is at least 31% and less than 60% of a projected areaof the vibration plane.
 6. The speaker grille of claim 1, wherein thespeaker is provided with a vibration plane of an oblong round shape, aneffective open area of the sound opening is at least 22% and less than60% of a projected area of the vibration plane.
 7. The speaker grille ofclaim 6, wherein the effective open area of the sound opening is atleast 48% and less than 60% of the projected area of the vibrationplane.
 8. The speaker grille of claim 1, wherein the speaker is providedwith a vibration plane of an oblong round shape, the sound opening isone of a plurality of sound openings, the reinforcement rib has portionsfor separating the sound openings in a direction of a shorter side ofthe vibration plane.
 9. The speaker grille of claim 8, further providedwith a block portion for blocking a central portion of the vibrationplane at the middle with respect to a longer side of the vibrationplane.
 10. The speaker grille of claim 9, further provided with a magneton a surface of the block portion, the surface opposing to the vibrationplane.
 11. The speaker grille of claim 1, wherein the speaker isprovided with a vibration plane of an oblong round shape, the soundopening is one of two sound openings, the reinforcement rib has a firstportion extending in a direction of a longer side of the vibration planeand disposed at the middle with respect to the direction of the shorterside of the vibration plane, the first portion separating the two soundopenings in a direction of a shorter side of the vibration plane. 12.The speaker grille of claim 11, wherein the reinforcement rib furtherhas second portions in the direction of the shorter side of thevibration plane for further splitting each of the two sound openings.13. The speaker grille of claim 11, further provided with a magnet on asurface of the first portion, the surface opposing to the vibrationplane.